Null function doesn't work with the 'upload file' fields

Null function doesn't work with the 'upload file' fields

Hi,

I have a form with an optional field 'upload a file'

If a user uploads the file, then I'd like my script to run some code. Here's my script:

if(input.Upload_File != null)
{
//run some code
}

The problem is that [some code] is run every time, no matter whether the user uploads the file or not. Is there a bug or am I doing something wrong?

Thanks!